An artificial diet, made up principally of chemicals set in agar, has given good growth in the sea hare Aplysia dactylomela Rang (13 and 29% increases in live weight in two trials of 24- and 16-day periods, respectively, at 28.5 °C). Spawn production accounted for 65 and 29%, respectively, of these increases in weight. The role that such a diet may play in the study of nutrition and feeding preferences of sea hares and of other marine invertebrate herbivores is discussed.